1. Field of the Invention
The present invention relates to a method for producing a semiconductor device using a Group III nitride-based compound semiconductor.
2. Description of the Related Art
In recent years, a blue-light semiconductor laser using a Group III nitride semiconductor such as GaN has been extensively developed. Such a blue-light semiconductor laser can be used as a light source for an optical disk reproduction apparatus.
In the case of producing a blue-light semiconductor laser, it is sometimes required alternately to repeat crystal growth in a vacuum apparatus and an operation in the air. For example, in the case of producing an embedded ridge type laser, a Group III nitride semiconductor layer is formed on a substrate in a vacuum apparatus, and then, the substrate is exposed to the air to form a current confinement layer. Thereafter, the substrate is placed again in the vacuum apparatus, and another Group III nitride semiconductor layer is grown on the Group III nitride semiconductor layer. In this case, an oxide layer is formed or impurities adhere to the surface of the first semiconductor layer during exposure to the air. Therefore, it is particularly important to conduct surface treatment of the first semiconductor layer after exposure to the air. In the surface treatment, it is required to remove the oxide layer and the impurities adhering to the surface of the semiconductor layer while preventing the surface of the semiconductor layer from being roughened.
Conventionally, a method for treating the surface of a Group III nitride semiconductor layer has been reported. For example, a method has been reported for treating a substrate, on which a semiconductor layer made of GaN is formed by epitaxial growth, (hereinafter, referred to as an xe2x80x9cepitaxial substratexe2x80x9d), using heated concentrated phosphoric acid. Further, a method has been reported for electrolytically etching an epitaxial substrate in an alkaline solution. Further, a method has been reported for etching an epitaxial substrate soaked in an alkaline solution by irradiating light having energy larger than the bandgap energy of GaN thereto (JP 9(1997)-232681). According to the method using an alkaline solution, an electric current is applied or light is radiated so as to increase an etching rate with respect to GaN.
However, according to a method for conducting surface treatment by using heated concentrated phosphoric acid, the surface flatness of a semiconductor layer is decreased due to the inconsistencies in the temperature of the heated concentrated phosphoric acid. Further, according to a method for etching in an alkaline solution, the surface flatness of a semiconductor layer also is decreased due to the local irregularities in a current or light irradiation. Such a decrease in the surface flatness of a semiconductor layer decreases the crystallinity of another Group III nitride semiconductor grown on an epitaxial substrate, which degrades the physical and electrical characteristics of a semiconductor device.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a method for producing a semiconductor device with high performance and reliability.
In order to achieve the above-mentioned object, the first method for producing a semiconductor device of the present invention includes: (i) heating a first semiconductor layer made of a Group III nitride-based compound semiconductor in gas containing nitrogen atoms; and (ii) after the process (i), growing a second semiconductor layer made of a Group III nitride-based compound semiconductor on the first semiconductor layer. According to the first method, an oxide layer and impurities adhering to the surface of the first semiconductor layer can be removed without degrading the flatness of the surface of the first semiconductor layer. Therefore, according to the first method, the second semiconductor layer with good crystallinity can be grown, whereby a semiconductor device with high performance and reliability can be produced.
According to the first method, the gas may contain at least one selected from the group consisting of nitrogen gas, ammonia, hydrazine, and a hydrazine derivative.
According to the first method, the first semiconductor layer may be heated at a temperature in a range of 500xc2x0 C. to 1000xc2x0 C. in the process (i).
Further, the second method for producing a semiconductor device of the present invention includes: (a) soaking a first semiconductor layer made of a Group III nitride-based compound semiconductor in an alkaline aqueous solution under a condition that, a current is not flowing through the first semiconductor layer; and (b) after the process (a), growing a second semiconductor layer made of a Group III nitride-based compound semiconductor on the first semiconductor layer. According to the second method, an oxide layer and impurities adhering to the surface of the first semiconductor layer can be removed without degrading the flatness of the surface of the first semiconductor layer. Therefore, according to the second method, the second semiconductor layer with good crystallinity can be grown, whereby a semiconductor device with high performance and reliability can be produced.
The second method further may include, after the process (a) and before the process (b), a heating process of heating the first semiconductor layer in gas containing nitrogen atoms. According to this structure, an oxide layer and moisture adhering to the surface of the first semiconductor layer during the process (a) can be removed, so that the second semiconductor layer with particularly good crystallinity can be formed.
According to the second method, the gas may contain at least one selected from the group consisting of nitrogen gas, ammonia, hydrazine, and a hydrazine derivative.
According to the second method, the first semiconductor layer may be heated at a temperature in a range of 500xc2x0 C. to 1000xc2x0 C. in the heating process.